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Eggshell

January 31, 2023

For other uses, see Eggshell (disambiguation).

An eggshell is the outer covering of a hard-shelled egg and of some forms of eggs with soft outer coats.

A broken wild bird eggshell

Diversity

Worm eggs

Nematode eggs present a two layered structure: an external vitellin layer made of chitin that confers mechanical resistance and an internal lipid-rich layer that makes the egg chamber impermeable.[1]

Insect eggs

 
Butterfly embryo / caterpillar visible through transparent eggshell

Insects and other arthropods lay a large variety of styles and shapes of eggs. Some of them have gelatinous or skin-like coverings, others have hard eggshells. Softer shells are mostly protein. It may be fibrous or quite liquid. Some arthropod eggs do not actually have shells, rather, their outer covering is actually the outermost embryonic membrane, the choroid, which serves to protect inner layers. The choroid itself can be a complex structure, and it may have different layers within it. It may have an outermost layer called an exochorion. Eggs which must survive in dry conditions usually have hard eggshells, made mostly of dehydrated or mineralized proteins with pore systems to allow respiration. Arthropod eggs can have extensive ornamentation on their outer surfaces.[citation needed]

Fish, amphibian and reptile eggs

Fish and amphibians generally lay eggs which are surrounded by the extraembryonic membranes but do not develop a shell, hard or soft, around these membranes. Some fish and amphibian eggs have thick, leathery coats, especially if they must withstand physical force or desiccation. These types of eggs can also be very small and fragile.[citation needed]

While many reptiles lay eggs with flexible, calcified eggshells, there are some that lay hard eggs. Eggs laid by snakes generally have leathery shells which often adhere to one another. Depending on the species, turtles and tortoises lay hard or soft eggs. Several species lay eggs which are nearly indistinguishable from bird eggs.[citation needed]

Bird eggs

 
This chicken egg has been soaked in vinegar for a few days and has become translucent and flexible.
 
Anatomy of a chicken egg.

The bird egg is a fertilized gamete (or, in the case of some birds, such as chickens, possibly unfertilized) located on the yolk surface and surrounded by albumen, or egg white. The albumen in turn is surrounded by two shell membranes (inner and outer membranes) and then the eggshell. The chicken eggshell is 95[citation needed]-97%[2] calcium carbonate crystals, which are stabilized by a protein matrix.[3][4][2] Without the protein, the crystal structure would be too brittle to keep its form and the organic matrix is thought to have a role in deposition of calcium during the mineralization process.[5][6][7] The structure and composition of the avian eggshell serves to protect the egg against damage and microbial contamination, prevention of desiccation, regulation of gas and water exchange for the growing embryo, and provides calcium for embryogenesis. Eggshell formation requires gram amounts of calcium being deposited within hours, which must be supplied via the hen's diet.[2]

 
Chicken egg with irregular calcification
 
Structure revealed by light

The fibrous chicken shell membranes are added in the proximal (white) isthmus of the oviduct.[2] In the distal (red) isthmus mammillae or mammillary knobs are deposited on the surface of the outer membrane in a regular array pattern.[8][9] The mammillae are proteoglycan-rich and are thought to control calcification. In the shell gland (similar to a mammalian uterus), mineralization starts at the mammillae. The shell gland fluid contains very high levels of calcium and bicarbonate ions. The thick calcified layer of the eggshell forms in columns from the mammillae structures, and is known as the palisade layer. Between these palisade columns are narrow pores that traverse the eggshell and allow gaseous exchange. The cuticle forms the final, outer layer of the eggshell.[10]

While the bulk of eggshell is made of calcium carbonate, it is now thought that the protein matrix has an important role to play in eggshell strength.[11] These proteins affect crystallization, which in turn affects the eggshell structure. Moreover, the concentration of eggshell proteins decreases over the life of the laying hen, as does eggshell strength.[citation needed]

In an average laying hen, the process of shell formation takes around 20 hours. Pigmentation is added to the shell by papillae lining the oviduct, coloring it any of a variety of colors and patterns depending on species. Since eggs are usually laid blunt end first, that end is subjected to most pressure during its passage and consequently shows the most color.[citation needed]

As they contain mainly calcium carbonate, bird eggshells dissolve in various acids, including the vinegar used in cooking. While dissolving, the calcium carbonate in an eggshell reacts with the acid to form carbon dioxide.[12]

Environmental issues

The US food industry generates 150,000 tons of shell waste per year.[13] The disposal methods for waste eggshells are 26.6% as fertilizer, 21.1% as animal feed ingredients, 26.3% discarded in municipal dumps, and 15.8% used in other ways.[14] Many landfills are unwilling to take the waste because the shells and the attached membrane attract vermin.[citation needed] Together with the calcium carbonate eggshell and protein-rich membrane are useless.[15] Recent inventions have allowed for the egg cracking industry to separate the eggshell from the eggshell membrane. The eggshell is mostly made up of calcium carbonate and the membrane is valuable protein. When separated both products have an array of uses.[citation needed]

Mammal eggs

Monotremes, egg-laying mammals, lay soft-shelled eggs similar to those of reptiles. The shell is deposited on the egg in layers within the uterus. The egg can take up fluids and grow in size during this process, and the final, most rigid layer is not added until the egg is full-size.[citation needed]

Egg teeth

Hatching birds, amphibian and egg-laying reptiles have an egg-tooth used to start an exit hole in the hard eggshell.[16][17]

Use

Eggshell waste is fundamentally composed of calcium carbonate, and has the potential to be used as raw material in the production of lime.[18]

Pharmaceuticals

The rich calcium carbonate shell has been used in the application for calcium deficiency therapies in humans and animals.[14][19] A single eggshell has a mass of six grams which yields around 2200 mg of calcium (6000 mg × 0.95 × 0.4= 2280 mg). Eggshell particles are used in toothpaste as an anti-tartar agent.[14] Powdered eggshells have been used for bone mineralization and growth.[14][20][19]

Food industry

Recent applications of eggshells include producing calcium lactate as a firming agent, a flavor enhancer, a leavening agent, a nutrient supplement, a stabilizer, and thickener.[14][19] Eggshells are also used as a calcium supplement in orange juice.[13]

Other uses

Eggshells have been incorporated into fertilizers as a soil conditioner.[14][21] They have also been used as a supplement to animal feed.[14][21] More recently the egg calcium carbonate particles have been used as coating pigments for ink-jet printing.[21] Powdered eggshells are also used in making paper pulp.[13] Recently eggshell waste has been used as a low cost catalyst for biodiesel production.[20] Chicken eggshells have been additionally incorporated as a calcium precursor into the synthesis of calcium-based metal-organic frameworks (MOFs).[22]

Recently, researchers have utilized chicken eggshells as a biofiller with a conducting polymer to enhance its sensing properties. Typically, eggshells were used as biofiller in polyaniline matrix to detect ammonia gas. The optimum ratio between eggshells and polyaniline could enhance this sensor measurement.[23]

See also

References

  1. ^ Benenati G, Penkov S, Müller-Reichert T, Entchev EV, Kurzchalia TV (May–Jun 2009). "Two cytochrome P450s in Caenorhabditis elegans are essential for the organization of eggshell, correct execution of meiosis and the polarization of embryo". Mech Dev. 126 (5–6): 382–93. doi:10.1016/j.mod.2009.02.001. PMID 19368796.
  2. ^ a b c d Hunton, P (2005). "Research on eggshell structure and quality: an historical overview". Revista Brasileira de Ciência Avícola. 7 (2): 67–71. doi:10.1590/S1516-635X2005000200001.
  3. ^ Arias, J. L.; Fernandez, M. S. (2001). "Role of extracellular matrix molecules in shell formation and structure". World's Poultry Science Journal. 57 (4): 349–357. doi:10.1079/WPS20010024. hdl:10533/197482. S2CID 86152776.
  4. ^ Nys, Yves; Gautron, Joël; Garcia-Ruiz, Juan M.; Hincke, Maxwell T. (2004). "Avian eggshell mineralization: biochemical and functional characterization of matrix proteins". Comptes Rendus Palevol. 3 (6–7): 549–62. doi:10.1016/j.crpv.2004.08.002.
  5. ^ Romanoff, A.L., A.J. Romanoff (1949) The avian egg. New York, Wiley.
  6. ^ Burley, R.W., D.V. Vadehra (1989) The Avian Egg: Chemistry and Biology. New York, Wiley.
  7. ^ Lavelin, I; Meiri, N; Pines, M (2000). "New insight in eggshell formation". Poultry Science. 79 (7): 1014–7. CiteSeerX 10.1.1.335.6360. doi:10.1093/ps/79.7.1014. PMID 10901204.
  8. ^ Wyburn, GM; Johnston, HS; Draper, MH; Davidson, MF (1973). "The ultrastructure of the shell forming region of the oviduct and the development of the shell of Gallus domesticus". Quarterly Journal of Experimental Physiology and Cognate Medical Sciences. 58 (2): 143–51. PMID 4487964.
  9. ^ Fernandez, MS; Araya, M; Arias, JL (1997). "Eggshells are shaped by a precise spatio-temporal arrangement of sequentially deposited macromolecules". Matrix Biology. 16 (1): 13–20. doi:10.1016/s0945-053x(97)90112-8. PMID 9181550.
  10. ^ "The Egg-Shell Microstructure Studied by Powder Diffraction". Xray.cz. Retrieved 2012-10-16.
  11. ^ http://ict.udg.co.cu/FTPDocumentos/Literatura%20Cientifica/Maestria%20Nutricion%20Animal/6.%20EVENTOS%20RELEVANTES/XVII%20Congreso%20Avicultura/confs/hunton1.htm. Retrieved February 2, 2011. {{cite web}}: Missing or empty |title= (help)[dead link]
  12. ^ "Q & A: Eggshells in Vinegar - What happened? | Department of Physics | University of Illinois at Urbana-Champaign". Van.physics.illinois.edu. 2007-10-22. Retrieved 2012-10-16.
  13. ^ a b c Hecht J: Eggshells break into collagen market. New Scientist 1999, 161:6-6.
  14. ^ a b c d e f g Daengprok W, Garnjanagoonchorn W, Mine Y: Fermented pork sausage fortified with commercial or hen eggshell calcium lactate. Meat Science 2002, 62:199-204.
  15. ^ Wei Z; Li B; Xu C (2009). "Application of waste eggshell as low-cost solid catalyst for biodiesel production". Bioresource Technology. 100 (11): 2883–2885. doi:10.1016/j.biortech.2008.12.039. PMID 19201602.
  16. ^ . Ag.ansc.purdue.edu. Archived from the original on 2012-12-08. Retrieved 2012-10-16.
  17. ^ Nys, Yves; Gautron, Joël; Garcia-Ruiz, Juan M.; Hincke, Maxwell T. (2004). "Avian eggshell mineralization: biochemical and functional characterization of matrix proteins" (PDF). Comptes Rendus Palevol. 3 (6–7): 549–562. doi:10.1016/j.crpv.2004.08.002.
  18. ^ Ferraz, Eduardo; Gamelas, José A. F.; Coroado, João; Monteiro, Carlos; Rocha, Fernando (2018-09-03). "Eggshell waste to produce building lime: calcium oxide reactivity, industrial, environmental and economic implications". Materials and Structures. 51 (5). doi:10.1617/s11527-018-1243-7. ISSN 1359-5997. S2CID 139375677.
  19. ^ a b c Daengprok W, Issigonis K, Mine Y, Pornsinpatip P, Garnjanagoonchorn W, Naivikul O: Chicken eggshell matrix proteins enhance calcium transport in the human intestinal epithelial cells, Caco-Journal of Agricultural and Food Chemistry 2003, 51:6056-6061.
  20. ^ a b Wei Z, Li B, Xu C: Application of waste eggshell as low-cost solid catalyst for biodiesel production [electronic resource]. Bioresource Technology 2009, 100:2883-2885.
  21. ^ a b c Yoo S, Kokoszka J, Zou P, Hsieh JS: Utilization of calcium carbonate particles from eggshell waste as coating pigments for ink-jet printing paper [electronic resource]. Bioresource Technology 2009, 100:6416-6421.
  22. ^ Crickmore, Tom S.; Sana, Haamidah Begum; Mitchell, Hannah; Clark, Molly; Bradshaw, Darren (2021-10-12). "Toward sustainable syntheses of Ca-based MOFs". Chemical Communications. 57 (81): 10592–10595. doi:10.1039/D1CC04032D. ISSN 1364-548X. S2CID 237628392.
  23. ^ N A Mazlan, J M Sapari, K P Sambasevam, Synthesis and fabrication of polyaniline/eggshell composite in ammonia detection, Journal of Metals, Materials and Minerals, Vol 30, No. 2, 50-57 (2020).https://ojs.materialsconnex.com/index.php/jmmm/article/view/649

Further reading

  • Kilner, R. M. (2006). "The evolution of egg colour and patterning in birds". Biological Reviews. 81 (3): 383–406. CiteSeerX 10.1.1.565.8957. doi:10.1017/S1464793106007044. PMID 16740199. S2CID 21083885.

External links

  • Fossil eggshells
  • Feeding for Stronger Egg Shells

January 31, 2023
eggshell, other, uses, disambiguation, eggshell, outer, covering, hard, shelled, some, forms, eggs, with, soft, outer, coats, broken, wild, bird, eggshell, contents, diversity, worm, eggs, insect, eggs, fish, amphibian, reptile, eggs, bird, eggs, environmental. For other uses see Eggshell disambiguation An eggshell is the outer covering of a hard shelled egg and of some forms of eggs with soft outer coats A broken wild bird eggshell Contents 1 Diversity 1 1 Worm eggs 1 2 Insect eggs 1 3 Fish amphibian and reptile eggs 1 4 Bird eggs 1 4 1 Environmental issues 1 5 Mammal eggs 1 6 Egg teeth 2 Use 2 1 Pharmaceuticals 2 2 Food industry 2 3 Other uses 3 See also 4 References 5 Further reading 6 External linksDiversity EditWorm eggs Edit Nematode eggs present a two layered structure an external vitellin layer made of chitin that confers mechanical resistance and an internal lipid rich layer that makes the egg chamber impermeable 1 Insect eggs Edit Butterfly embryo caterpillar visible through transparent eggshell Insects and other arthropods lay a large variety of styles and shapes of eggs Some of them have gelatinous or skin like coverings others have hard eggshells Softer shells are mostly protein It may be fibrous or quite liquid Some arthropod eggs do not actually have shells rather their outer covering is actually the outermost embryonic membrane the choroid which serves to protect inner layers The choroid itself can be a complex structure and it may have different layers within it It may have an outermost layer called an exochorion Eggs which must survive in dry conditions usually have hard eggshells made mostly of dehydrated or mineralized proteins with pore systems to allow respiration Arthropod eggs can have extensive ornamentation on their outer surfaces citation needed Fish amphibian and reptile eggs Edit Fish and amphibians generally lay eggs which are surrounded by the extraembryonic membranes but do not develop a shell hard or soft around these membranes Some fish and amphibian eggs have thick leathery coats especially if they must withstand physical force or desiccation These types of eggs can also be very small and fragile citation needed While many reptiles lay eggs with flexible calcified eggshells there are some that lay hard eggs Eggs laid by snakes generally have leathery shells which often adhere to one another Depending on the species turtles and tortoises lay hard or soft eggs Several species lay eggs which are nearly indistinguishable from bird eggs citation needed Bird eggs Edit This chicken egg has been soaked in vinegar for a few days and has become translucent and flexible Anatomy of a chicken egg The bird egg is a fertilized gamete or in the case of some birds such as chickens possibly unfertilized located on the yolk surface and surrounded by albumen or egg white The albumen in turn is surrounded by two shell membranes inner and outer membranes and then the eggshell The chicken eggshell is 95 citation needed 97 2 calcium carbonate crystals which are stabilized by a protein matrix 3 4 2 Without the protein the crystal structure would be too brittle to keep its form and the organic matrix is thought to have a role in deposition of calcium during the mineralization process 5 6 7 The structure and composition of the avian eggshell serves to protect the egg against damage and microbial contamination prevention of desiccation regulation of gas and water exchange for the growing embryo and provides calcium for embryogenesis Eggshell formation requires gram amounts of calcium being deposited within hours which must be supplied via the hen s diet 2 Chicken egg with irregular calcification Structure revealed by light The fibrous chicken shell membranes are added in the proximal white isthmus of the oviduct 2 In the distal red isthmus mammillae or mammillary knobs are deposited on the surface of the outer membrane in a regular array pattern 8 9 The mammillae are proteoglycan rich and are thought to control calcification In the shell gland similar to a mammalian uterus mineralization starts at the mammillae The shell gland fluid contains very high levels of calcium and bicarbonate ions The thick calcified layer of the eggshell forms in columns from the mammillae structures and is known as the palisade layer Between these palisade columns are narrow pores that traverse the eggshell and allow gaseous exchange The cuticle forms the final outer layer of the eggshell 10 While the bulk of eggshell is made of calcium carbonate it is now thought that the protein matrix has an important role to play in eggshell strength 11 These proteins affect crystallization which in turn affects the eggshell structure Moreover the concentration of eggshell proteins decreases over the life of the laying hen as does eggshell strength citation needed In an average laying hen the process of shell formation takes around 20 hours Pigmentation is added to the shell by papillae lining the oviduct coloring it any of a variety of colors and patterns depending on species Since eggs are usually laid blunt end first that end is subjected to most pressure during its passage and consequently shows the most color citation needed As they contain mainly calcium carbonate bird eggshells dissolve in various acids including the vinegar used in cooking While dissolving the calcium carbonate in an eggshell reacts with the acid to form carbon dioxide 12 Environmental issues Edit The US food industry generates 150 000 tons of shell waste per year 13 The disposal methods for waste eggshells are 26 6 as fertilizer 21 1 as animal feed ingredients 26 3 discarded in municipal dumps and 15 8 used in other ways 14 Many landfills are unwilling to take the waste because the shells and the attached membrane attract vermin citation needed Together with the calcium carbonate eggshell and protein rich membrane are useless 15 Recent inventions have allowed for the egg cracking industry to separate the eggshell from the eggshell membrane The eggshell is mostly made up of calcium carbonate and the membrane is valuable protein When separated both products have an array of uses citation needed Mammal eggs Edit Monotremes egg laying mammals lay soft shelled eggs similar to those of reptiles The shell is deposited on the egg in layers within the uterus The egg can take up fluids and grow in size during this process and the final most rigid layer is not added until the egg is full size citation needed Egg teeth Edit Hatching birds amphibian and egg laying reptiles have an egg tooth used to start an exit hole in the hard eggshell 16 17 Use EditEggshell waste is fundamentally composed of calcium carbonate and has the potential to be used as raw material in the production of lime 18 Pharmaceuticals Edit The rich calcium carbonate shell has been used in the application for calcium deficiency therapies in humans and animals 14 19 A single eggshell has a mass of six grams which yields around 2200 mg of calcium 6000 mg 0 95 0 4 2280 mg Eggshell particles are used in toothpaste as an anti tartar agent 14 Powdered eggshells have been used for bone mineralization and growth 14 20 19 Food industry Edit Recent applications of eggshells include producing calcium lactate as a firming agent a flavor enhancer a leavening agent a nutrient supplement a stabilizer and thickener 14 19 Eggshells are also used as a calcium supplement in orange juice 13 Other uses Edit Eggshells have been incorporated into fertilizers as a soil conditioner 14 21 They have also been used as a supplement to animal feed 14 21 More recently the egg calcium carbonate particles have been used as coating pigments for ink jet printing 21 Powdered eggshells are also used in making paper pulp 13 Recently eggshell waste has been used as a low cost catalyst for biodiesel production 20 Chicken eggshells have been additionally incorporated as a calcium precursor into the synthesis of calcium based metal organic frameworks MOFs 22 Recently researchers have utilized chicken eggshells as a biofiller with a conducting polymer to enhance its sensing properties Typically eggshells were used as biofiller in polyaniline matrix to detect ammonia gas The optimum ratio between eggshells and polyaniline could enhance this sensor measurement 23 See also EditEggshell skull rule in tort law Walk on eggshells an idiom in the English language Eggshell membrane a dietary supplementReferences Edit Benenati G Penkov S Muller Reichert T Entchev EV Kurzchalia TV May Jun 2009 Two cytochrome P450s in Caenorhabditis elegans are essential for the organization of eggshell correct execution of meiosis and the polarization of embryo Mech Dev 126 5 6 382 93 doi 10 1016 j mod 2009 02 001 PMID 19368796 a b c d Hunton P 2005 Research on eggshell structure and quality an historical overview Revista Brasileira de Ciencia Avicola 7 2 67 71 doi 10 1590 S1516 635X2005000200001 Arias J L Fernandez M S 2001 Role of extracellular matrix molecules in shell formation and structure World s Poultry Science Journal 57 4 349 357 doi 10 1079 WPS20010024 hdl 10533 197482 S2CID 86152776 Nys Yves Gautron Joel Garcia Ruiz Juan M Hincke Maxwell T 2004 Avian eggshell mineralization biochemical and functional characterization of matrix proteins Comptes Rendus Palevol 3 6 7 549 62 doi 10 1016 j crpv 2004 08 002 Romanoff A L A J Romanoff 1949 The avian egg New York Wiley Burley R W D V Vadehra 1989 The Avian Egg Chemistry and Biology New York Wiley Lavelin I Meiri N Pines M 2000 New insight in eggshell formation Poultry Science 79 7 1014 7 CiteSeerX 10 1 1 335 6360 doi 10 1093 ps 79 7 1014 PMID 10901204 Wyburn GM Johnston HS Draper MH Davidson MF 1973 The ultrastructure of the shell forming region of the oviduct and the development of the shell of Gallus domesticus Quarterly Journal of Experimental Physiology and Cognate Medical Sciences 58 2 143 51 PMID 4487964 Fernandez MS Araya M Arias JL 1997 Eggshells are shaped by a precise spatio temporal arrangement of sequentially deposited macromolecules Matrix Biology 16 1 13 20 doi 10 1016 s0945 053x 97 90112 8 PMID 9181550 The Egg Shell Microstructure Studied by Powder Diffraction Xray cz Retrieved 2012 10 16 http ict udg co cu FTPDocumentos Literatura 20Cientifica Maestria 20Nutricion 20Animal 6 20EVENTOS 20RELEVANTES XVII 20Congreso 20Avicultura confs hunton1 htm Retrieved February 2 2011 a href Template Cite web html title Template Cite web cite web a Missing or empty title help dead link Q amp A Eggshells in Vinegar What happened Department of Physics University of Illinois at Urbana Champaign Van physics illinois edu 2007 10 22 Retrieved 2012 10 16 a b c Hecht J Eggshells break into collagen market New Scientist 1999 161 6 6 a b c d e f g Daengprok W Garnjanagoonchorn W Mine Y Fermented pork sausage fortified with commercial or hen eggshell calcium lactate Meat Science 2002 62 199 204 Wei Z Li B Xu C 2009 Application of waste eggshell as low cost solid catalyst for biodiesel production Bioresource Technology 100 11 2883 2885 doi 10 1016 j biortech 2008 12 039 PMID 19201602 What is Egg Shell Quality and How to Preserve It Ag ansc purdue edu Archived from the original on 2012 12 08 Retrieved 2012 10 16 Nys Yves Gautron Joel Garcia Ruiz Juan M Hincke Maxwell T 2004 Avian eggshell mineralization biochemical and functional characterization of matrix proteins PDF Comptes Rendus Palevol 3 6 7 549 562 doi 10 1016 j crpv 2004 08 002 Ferraz Eduardo Gamelas Jose A F Coroado Joao Monteiro Carlos Rocha Fernando 2018 09 03 Eggshell waste to produce building lime calcium oxide reactivity industrial environmental and economic implications Materials and Structures 51 5 doi 10 1617 s11527 018 1243 7 ISSN 1359 5997 S2CID 139375677 a b c Daengprok W Issigonis K Mine Y Pornsinpatip P Garnjanagoonchorn W Naivikul O Chicken eggshell matrix proteins enhance calcium transport in the human intestinal epithelial cells Caco Journal of Agricultural and Food Chemistry 2003 51 6056 6061 a b Wei Z Li B Xu C Application of waste eggshell as low cost solid catalyst for biodiesel production electronic resource Bioresource Technology 2009 100 2883 2885 a b c Yoo S Kokoszka J Zou P Hsieh JS Utilization of calcium carbonate particles from eggshell waste as coating pigments for ink jet printing paper electronic resource Bioresource Technology 2009 100 6416 6421 Crickmore Tom S Sana Haamidah Begum Mitchell Hannah Clark Molly Bradshaw Darren 2021 10 12 Toward sustainable syntheses of Ca based MOFs Chemical Communications 57 81 10592 10595 doi 10 1039 D1CC04032D ISSN 1364 548X S2CID 237628392 N A Mazlan J M Sapari K P Sambasevam Synthesis and fabrication of polyaniline eggshell composite in ammonia detection Journal of Metals Materials and Minerals Vol 30 No 2 50 57 2020 https ojs materialsconnex com index php jmmm article view 649Further reading EditKilner R M 2006 The evolution of egg colour and patterning in birds Biological Reviews 81 3 383 406 CiteSeerX 10 1 1 565 8957 doi 10 1017 S1464793106007044 PMID 16740199 S2CID 21083885 External links EditFossil eggshells Feeding for Stronger Egg Shells Retrieved from https en wikipedia org w index php title Eggshell amp oldid 1136308875, wikipedia, wiki, book, books, library,

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